Luminescence optimization with superior asymmetric ratio (red/orange) and color purity of MBO3:Eu3+@SiO2 (M = Y, Gd and Al) nano down-conversion phosphors

Abstract

Y_1−xBO₃:Eu_x³⁺ (0.07 ≤ x ≤ 0.5 moles) and Y_0.7−2x (Gd_x, Al_x)BO₃:Eu³⁺_0.3 (0.05 ≤ x ≤ 0.3 moles) powder phosphors have been synthesized by a novel co-precipitation technique followed by heat treatment. Luminescence optimization was carried out by optimizing the dopant Eu³⁺ concentration, substitution of Y³⁺ with Gd³⁺/Al³⁺ and finally with SiO₂ shell coating. The inversion symmetry of Eu³⁺ ions were lowered with Eu³⁺ concentration and substitution of Y³⁺ with Gd³⁺/Al³⁺, respectively. It has been noted that the intensity behavior of PL peaks of Eu³⁺:⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂ are not only sensitive to the inversion symmetry of Eu³⁺ ions, but also to the monitoring excitation wavelengths. Due to nanosize particle distribution, the optimum activator (Eu³⁺) concentration (30 mol%) was found to be extremely at higher level, compared to the bulk phosphors. The asymmetric ratio (red/orange) and color purity of the optimized phosphors, Y_0.7BO₃:Eu_0.3³⁺ (with crystallite size, D = 32 nm) and Y_0.3Gd_0.2Al_0.2BO₃:Eu³⁺ (D = 17 nm) were further enhanced with an SiO₂ coating. Based on the systematic study, the nanophosphor Y_0.7BO₃:Eu_0.3³⁺@SiO₂ with an R/O ratio as 6.710 and color coordinates (x = 0.6612, y = 0.3357) is optimized as a remarkable phosphor having superior features than the commercial, available literature data results.